Multi-head press data delivery rate control

ABSTRACT

In a printing method and systems, segments of a first print job are distributed to respective downstream processors and are processed to provide printable frames, which are stored in respective print queues. Each print queue supplies a respective one or more printheads. The printable frames are sequentially printed on a continuously transported receiver. A maximum printing duration of each of the print queues is computed periodically during the printing. The transport speed is regulated to trend the maximum printing durations toward a predetermined baseline. The sending of a second print job to the downstream processors is delayed, while processing of the first print job is completed. The delaying is counter to the regulating and reduces the print queues of the first print job non-uniformly relative to the baseline.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned, co-pending U.S. patentapplication Ser. No. 11/782,670, now U.S. Publication Ser. No.2009/0027714, entitled: JOB STARTUP CONTROL FOR JOB QUEUING, filed Jul.25, 2007, in the names of William C. Kuhn and Paul A. Reil, which ishereby incorporated herein by reference.

Reference is made to commonly assigned, co-pending U.S. patentapplication Ser. No. 11/782,680, now U.S. Publication Ser. No.2009/0027715, entitled: FAST JOB HALT IN A HIGH SPEED PRESS, filed Jul.25, 2007, in the names of William C. Kuhn and Paul A. Reil, which ishereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to high speed printing systems and methods andmore particularly relates to multi-head press data delivery ratecontrol.

BACKGROUND OF THE INVENTION

Very high speed commercial digital presses print variable data at ratesof thousands of pages per minute. Typically, the receiver that isprinted is in the form of a web that is transported past stationaryprintheads. During transport, the web has considerable inertia andcannot be readily subjected to rapid changes in speed. It is desirableto continuously transport the web at a constant speed or with relativelyslow speed adjustments.

The continuous transport of receiver also necessitates a continuoussupply of data in the form of printable frames. This data must bebuffered so as to be available as needed. Considerable time is requiredto fill a buffer with the printable frames, since the print job isinitially supplied in a different form and is converted. That conversionis typically in the form of raster image processing and is performed byone or more downstream processors. The processing speed that defines thesustained output speed of each of the downstream processors is generallylimited by the content of the input data, since the time to raster imageprocess a frame tends to be highly data dependant. It is possible todefine frames that take a substantial amount of time to prepare foroutput. Another limitation that affects the raster image processing isthe supply of input data to the downstream processors. Variable datasupplied by a secondary source can be subject to limitations ofcommunication bandwidth or the processing capability of a host computer.With many print jobs, different portions of the job are simultaneouslybuffered, being raster image processed, and not yet delivered to theraster image processor.

It would thus be desirable to provide improved systems and methods.

SUMMARY OF THE INVENTION

In high speed and very high speed printing, a continuing problem issupplying data at a rate sufficiently matched to the print engine. Oneapproach to solving this problem is pausing transport of a receiverthrough a path until data is available. This approach can beproblematic, particularly with a receiver in the form of a web and athigh rates of transport. Another approach is to restrict how a print jobis input. This is workable, but greatly encumbers making any last minutechanges. U.S. Pat. No. 6,762,855 discloses a system that uses buffermanagement logic to adjust transport speed on a per-document basis.Control buffers accumulate slack time left over from raster imageprocessing non-complex documents and then allocate that slack time tocomplex documents to optimize average raster image processing time withthe speed of the print engine. This patent does not address controllingdelivery of data from multiple, queued print jobs to prevent a laterprint job from damaging an earlier unfinished print job.

The invention, which is defined by the claims, is directed toameliorating the above problems. The invention, in broader aspects,provides printing method and systems, in which segments of a first printjob are distributed to respective downstream processors and areprocessed to provide printable frames, which are stored in respectiveprint queues. Each print queue supplies a respective one or moreprintheads. The printable frames are sequentially printed on acontinuously transported receiver. A maximum printing duration of eachof the print queues is computed periodically during the printing. Thetransport speed is regulated to trend the maximum printing durationstoward a predetermined baseline. The sending of a second print job tothe downstream processors is delayed, while processing of the firstprint job is completed. The delaying is counter to the regulating andreduces the print queues of the first print job non-uniformly relativeto the baseline.

It is an advantageous effect of the invention that improved systems andmethods are provided, in which receiver transport speed is regulatedtaking into account print job queuing and high speed or very high speedtransport.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be better understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying figures wherein:

FIG. 1 is a diagrammatical view of an embodiment of the systems.

FIG. 2 is a partial detail of the view of FIG. 1 showing the maincontroller and downstream processors of the data control unit.

FIG. 3 is a diagram illustrating operation of a specific embodiment ofthe apparatus of the system of FIG. 1.

FIG. 4 is a diagram illustrating part of the operation of FIG. 3, asmodified in a specific embodiment.

FIG. 5 is a diagram illustrating operation of another specificembodiment of the apparatus of the system of FIG. 1.

FIG. 6 is a diagram of an embodiment of a job startup control method.

FIG. 7 is a diagram of an embodiment of a fast job halt method.

FIG. 8 is a diagram of an embodiment of a data delivery rate controlmethod.

DETAILED DESCRIPTION OF THE INVENTION

High speed variable printing systems are used in the commercial printingindustry for printing a wide variety of printing applications fromprinting short run catalogs, and advertisements to printingtransactional printed products such as billings and investment reports.

Referring to FIG. 1, the system 200 has a press (indicated by dashedline 212) that prints on a receiver 214. The term “receiver” refers tomedia that accepts a printed image and is singular or plural, asindicated by context. A receiver can be multiple cut-sheets. Inparticular embodiments discussed herein, the receiver is in the form ofa web, that is an elongate, continuous piece. The use of a web typicallyallows the press (also referred to herein as a printer) to attain higherspeeds in transport, than other forms of receiver, such as cut-sheets.The receiver is typically paper, but can also be any of a large numberof other types of print media. For example, the receiver can be thin orthick paper stock (coated or uncoated) or transparency stock. Thereceiver has opposed first and second surfaces 214 a, 214 b one or bothof which may be printed.

The receiver 214 in FIG. 1 is a web. The web is moved from a supply 201to a take-up 203 by a transport 205. Between the supply 201 and take-up203, the web is threaded around a number of rollers 216 and past asequence of printheads 218. The printheads can be continuous ink jetprintheads, drop on demand ink jet printheads, electrophotographictoning stations (with or without transfer rollers or the like), or otherequivalent units of a variable printing technology. For simplicity, inthe discussion here, the printheads are generally discussed in terms ofan embodiment, in which all of the printheads arranged in a sequence andeach printhead extends across the full width of the receiver. It will beunderstood that like considerations apply to other embodiments. Forexample, instead of using a full width printhead, a group of printheadscan be arranged in parallel (non-sequentially) to print a widerreceiver.

The different printheads each print a printable frame. A unit of imagedata that corresponds to a frame is referred to herein as a “segment”.The frames are printed in registry with each other and, in combination,provide a document. The term “document” as used herein, thus,corresponds to the term “page”, in ordinary usage and includes bothsurfaces. (The term “page” is sometimes also used in the art as atechnical term to refer to a frame, and is generally avoided here forthat reason.) Each frame can define an image area corresponding to thefull dimensions as the document or can define a smaller area withinthose dimensions. Each frame represents a part of a document that isconveniently printed separately. For example, each frame can use adifferent color of ink. With ink jet printheads, different frames can beused to divide an image into different patterns of relatively spacedapart deposited drops. The resulting combined image is unchanged, butthe different patterns improve drying, during the printing process. Twosets of four printheads 218 are shown in FIG. 1. The invention is notlimited as to a particular number of printheads or sets of printheads.In FIG. 1, after passing one set of printheads 218, the partiallyprinted image (not shown) on a first side 214 b of the receiver 214 isdried by contact with a first heated drum dryer 220. The web is thenflipped over by a turn station 222 before passing the second set ofprintheads 218 and the second side 214 a is then dried by a second dryer221.

In use, printing data is first supplied to a data station 224 by one ormore input units 226 from one or more image data sources. The datastation includes at least some of the functions necessary to prepare thejob data for the printheads and can optionally combine all of thefunctions in a single unit. The data station can also provide a systemmanager and user interface (not separately illustrated). The systemmanager provides a communication hub, and system level administrationand control features for other system components. The user interfaceprovides setup and status information for the operation of the system.Via this interface, the user can input to the controller the physicalcharacteristics of the printer, such as the relationships of theprintheads, desired colors the system is capable of printing, and otherinformation. Upon a power-up or a reset, the data station initializesthe system to a ready state.

As discussed further below, the job data can be a single print job or aseries of print jobs. The printing data represents the location, color,and intensity of each pixel that is exposed and is in the form of one ormore data files, which typically include or are accompanied by controlcommands. For example, data files can be supplied in a PDL (pagedescription language) format, such as Postscript or IPDS or IJPDS.Printing data can be supplied from multiple sources, for combinationduring printing. U.S. Pat. No. 5,729,665, issued to Gauthier, disclosesan example of this type of procedure. One input unit 226 is typically alocally connected host computer capable of supplying the printing datain a continuous stream. Software controls the flow of data from the hostcomputer and via a host interface. The connection between the datastation and the host computer can be uni-directional or can bebi-directional to allow status information and the like to be presentedon a user interface of the host computer. Suitable software for thispurpose is well known to those of skill in the art. Other types of inputunit can be used instead of or in addition to a host computer. Forexample, printing data can be supplied by a media reader usingtransferable media, such as CD's, DVD's, or by network connection fromanother computer. An image data source is a device that can providedigital data defining a version of the image. Such types of devices arenumerous and include computers or microcontrollers, computerworkstations, scanners, and digital cameras. Multiple devices can beinterconnected on a network. These image data sources are at the frontend and generally include an application program that is used to createor find an image to output.

The job data is sent to a data control unit 227, which includes a maincontroller 228, a memory section 229, and a set of downstream processors234. The job data is sent to the main controller 228, either directly orvia input queue memory. The term “memory” refers to one or more suitablysized logical units of physical memory provided in semiconductor memoryor magnetic memory, or the like (illustrated by memory section 229). Aparticular queue in memory can be a logical division or physicaldivision of memory. If a logical division, the physical memory allocatedto that logical division can be in the same or different locations andcan change during use, without effecting the logical division. Likewise,a queue provided in a physical unit of memory can be altered logically,for example, by changing a pointer, to change the print queue duringuse. Memory can include conventional memory devices including solidstate, magnetic, optical or other data storage devices and can be fixedwithin system or can be removable. For example, memory can be aninternal memory, such as SDRAM or Flash EPROM memory, or alternately aremovable memory, or a combination of both. Removable memory can be ofany type, such as a Compact Flash (CF) or Secure Digital (SD) type cardinserted into a socket and connected to the processor via a memoryinterface. Other types of storage that are utilized include withoutlimitation PC-Cards, MultiMedia Cards (MMC), or embedded and/orremovable hard drives. Memory is also inclusive of a remote memorysystem such as a personal computer, computer network or other digitalsystem.

The use of queues is generally discussed herein in relation to movementof print jobs into and out of the print queues. It will be understoodthat, in some cases, movement of a print in or out of a queue willentrain division of the print job into separately movable portions.

The input queue can provide a large buffer, with a size determined bythe speed of the press. The input queue is handled by a control systemto supply sufficient data to the press to keep the press runningcontinuously and efficiently. The input queue control system can beprovided as a function of the main controller.

Referring to FIGS. 1-2, the main controller 228 has a supervisor 230that receives the job data and a job record processor 232 that segmentsthe job data and distributes the segments. The segments are eachdistributed to the appropriate downstream processor 234, which thensupplies the printhead 218 required by the data in the respectivesegment. Signal paths 236 run between the downstream processors 234 andthe respective printheads 218. The segments can be distributed to thedownstream processors in blocks, which may or may not correspond in sizeto particular segments. The segmentation and block divisions provided bythe job record processor can be as simple as identifying predeterminedpartitions in the print data or can require extensive computations.Suitable procedures for these purposes are well known to those of skillin the art.

The job record processor 232 also distributes commands necessary for therespective downstream processor and printhead. In a particularembodiment, the job record processor distributes the data to theindividual downstream processors via a data bus (item 31 in FIG. 3). Aprocessor buffer 29 can be used to store the segments between the jobrecord processor and the downstream processors. It is convenient if themain controller also handles errors in the input data. Suitable featuresfor this function are well known to those of skill in the art. Inaddition to distributing the segments, the job record processorprocesses control parameters (sometimes referred to as “input records”),which apply to the entire job. For example, the job record processorhandles the job control record, which is typically the first inputrecord and specifies the job name, number of downstream processors, andthe like.

The downstream processors receive the respective segments and convertthe commands and data into printable frames compatible with the press.The conversion generally includes raster image processing that isapplied to print data in the form of page description language toproduce bitmapped frames that are then printed without furthermodification, but the processing can differ and the printable frames canbe subject to further processing before printing. For example, thedownstream processors may receive pre-ripped bitmaps and simply convertthem into final form ready for output. Each downstream processorsupplies printable data to one or more printheads. As with othercomponents discussed herein, the downstream processors can each beprovided in the form of software or hardware or a combination of thetwo. In a particular embodiment, efficiency is improved by including oneor more microprocessors in each downstream processor used, with eachdownstream processor corresponding to one of the segments of a printjob. A user interface (not shown) to the downstream processors can beprovided, either directly or via the main controller, by which theconfiguration of the printer or the flow of the data can be set upand/or monitored.

Each downstream processor acknowledges receipt of the print data. Themain controller communicates bidirectionally with the individualdownstream processors to enable or disable the output, to configureoutput parameters such as printhead width and the number of pixels inthe paper motion direction per encoder pulses from the paper motionencoder and ripping parameters such as maximum frame length forregistration cued documents. The main controller also tracks the statusof each frame given to the downstream processors, and detects errorsfrom the downstream processors.

In a particular embodiment the functions of the downstream processorsare to receive the printing data, parse the header from the print joband determine the printing and finishing requirements of the job,analyze the PDL (page description language) to determine any job orframe requirements that were not stated in the header, resolve anyconflicts between the requirements of the job and the marking engineconfiguration (for example, raster image processing time or mismatchresolution), keep accounting record and error logs and provide thisinformation upon request, communicate image transfer requirements to themarking engine, translate the data from PDL (page description language)to raster for printing, and support diagnostics for maintenance and thelike. The raster image processor accepts a print job in the form of apage description language (PDL) such as IJPDS, IPDS, Postscript, PDF, orPCL and converts it into a raster or grid of lines or another form thatthe marking engine can accept.

The processing in the different downstream processors is asynchronous,that is, each downstream processor performs processing of a respectivesegment in a manner that is not synchronous with the processing of theother segments in the other downstream processors. Processing indifferent downstream processors in synchrony is not practical, in viewof communications delays, the effect of errors and the like, and thefact that processing time, particularly raster image processing, isdependent upon content of the respective segments. The processing of asegment in a downstream processor begins when one or more blockscontaining all or, alternatively, part of the segment are received bythe downstream processor.

The type of processing performed in the downstream processors can differbetween different print jobs provided in a stream of printing data. Thenumber of downstream processors used and the manner of their use (alsoreferred to herein as the “arrangement”) is a function of the content ofa particular print job. For example, a particular print job might notuse a printhead, due to not using the color of ink supplied by thatprinthead. Similarly, a press could have a pair of four-color,document-wide printheads. A first job might have an arrangement usingboth for all four colors, and a second job might have an arrangementusing one of the two printheads for two of the colors and the other headfor the other two.

Each downstream processor can be provided, in memory, with a respectiveprocessing or input queue and a respective print or output queue.Printing data in the processing queues is supplied to respectivedownstream processors as processing capacity becomes available. As withother queues described herein, compression/decompression can be used toreduce queue size (data volume in memory), within applicable timeconstraints and available processing capabilities.

The print queues supply the printheads. The data usage rate at theprintheads varies with the speed of transport of the receiver. In aparticular embodiment, shown in FIG. 3, during normal printing, thedownstream processor is able to produce bitmaps by raster imageprocessing faster than the bitmaps are printed. A print job 24 issupplied to the supervisor 230, which transfers the data to the jobrecord processor 232. An output control 27 of the main controller 228communicates bidirectionally with the supervisor 230 and the downstreamprocessors to enable or disable output, to configure output parameterssuch as printhead width, and frame length.

In FIG. 3, components related to supplying bitmapped frames to theprintheads are indicated by dashed lines 33-n. The downstream processor35 converts the image data to a bitmap and supplies the bitmapped frameto the print buffer 37, which provides the bitmapped frame as an output39 to the appropriate printing module controlling the respectiveprinthead. FIG. 4 shows these steps in more detail. The downstreamprocessor 35 creates a bitmapped frame, takes an empty unit of memoryfrom a free frame store 41, fills the empty memory unit with thebitmapped frame, and assigns the filled memory unit to the print queue43. The printhead prints the bitmapped frames in the print queue andthen the respective memory units are returned to the free frame store,which can be actual memory dedicated to this use or virtual memory madeavailable as needed.

The supplied bitmapped frames are printed by the printheads of thepress. In a particular embodiment, the system has continuous ink jetprintheads, in which each print head defines one or more rows oforifices which receive an electrically conductive recording fluid, suchas water based ink, from a pressurized fluid supply manifold and ejectthe fluid in rows of parallel streams. Printers using such print headsand print engines accomplish graphic reproduction by selectivelycharging and deflecting the drops in each of the streams and depositingat least some of the drops on a print receiving medium, while others ofthe drops strike a drop catcher device. The present invention is notlimited to any specific image transfer process or receiver type, but canbe applied to any high speed printing system including sheet-fedsystems. In a particular embodiment, the press is capable of printing asingle color A4 page up through two full across, duplex A4 pages in fullcyan, magenta, yellow, and black process color.

The bitmapped frames are received from respective print queues, by printmodules. Each print module is an output driver that drives the one ormore printheads that print the respective frames. Print modules areconveniently provided in the press, but like other components of thesystem, can be located separately or combined with other components.

The press has a transport unit that transports the receiver along a pathpast the printheads. In particular embodiments, the transport iscontinuous during the various steps of preparing and printing thedocument or documents of the print data. The printheads are sequentiallyarranged relative to the transport path, such that the printheadssequentially mark the receiver, adding respective printable frames inregistry to provide a printed output having one or more documents.

Suitable apparatus for use as the transport unit is well known to thoseof skill in the art. In a particular embodiment, the receiver is a paperweb and the transport unit has a transport controller, a receiversupply, a receiver collector, a drive, and a plurality of supportmembers. The transport controller is a programmable logic controller.The receiver supply is a core that holds a spool of the paper web. Thereceiver collector is a mandrel that is driven by the drive. The supportmembers include a plurality of rollers positioned to bear the web. Othertypes of support members, such as skis and bars, could be substitutedfor one or more of the rollers. The core and one or more of the supportmembers can also be driven. The receiver collector can collect the webin a roll, can use any suitable post print peripheral such as a folderor cutter, or can feed a production line for more complete finishing.

The main controller of the press includes a printing manager thatmonitors and controls the electromechanical aspects of the press,including image formation with the printheads and transport of thereceiver. The printing manager can be included within the printer or asall or part of a separate component. Appropriate sensors such asmechanical, electrical, or optical sensors can be utilized to check thestatus of different aspects of the system. For example, such sensors canbe located along the transport path of the receiver and can beassociated with the printheads. Based on such signals and a suitableprogram the printing manager can control the operation of the press.Suitable procedures and equipment for this purpose are known to those ofskill in the art.

In particular embodiments, the press includes a registration unit havingone or more registration cue sensors that detect the location ofregistration marks or cues. That location information is then used toregister the output of one or more printheads. Suitable techniques andequipment for this purpose is disclosed in U.S. Published PatentApplication No. US2003/0234959A1, which is hereby incorporated herein byreference. Misregistration between different frames of a document, atleast on the same document surface, is very noticeable. For that reason,in some embodiments the registration cues are printed by the printheadsproducing one or more of the frames of a document and are then used toregister one or more frames printed later in the sequence for thatdocument. Additional registration features can be provided on thereceiver or otherwise, to track receiver location and travel for use indefining a location of the document on the receiver.

The respective segments are transferred in registered relationship tothe receiver as the receiver is transported serially from printhead toprinthead, receiving at each printhead a respective frame of a document.The printheads operate in parallel, that is, different printheads printat the same time. Printheads can be located such that two or moredifferent printheads print the same document, that is the same compositepage, simultaneously or all printheads can print different documentssimultaneously. It will be appreciated that the timing of printing tothe receiver is such that proper transfer of images are made so thatrespective images are transferred in register and as expected.Adjustments of transport speed can be made on a continuous or steppedramp.

Job Startup Control

Referring now to FIG. 1, in the press, there is a considerable distancemeasured along the transport path between the first printhead and thelast printhead. As a result, the first printhead can print frames of alarge number of documents before the first such document arrives at thelast printhead, which prints one of the frames on the second side of thedocument. Similarly, at the end of a print job, printhead stops printinglong before printhead does. This becomes more complicated when theprinting data includes multiple print jobs, which can use differentnumbers and arrangements of printheads. Problems can occur ifconsecutive print jobs have different printhead configurations. Sincethe printheads are spread along the web, the printheads may or may notprinting the same document at any given time. Normally, all the data fora frame comes into the main controller at the same time. As a result,the printheads that print later have to be buffered by more data. Withmore complex documents, one or more printable frames may not yet beprocessed, while other frames of the same document are being deliveredfrom respective print queues for printing. When the printing data is astream of print jobs, the next job in the stream can be begun when adownstream processor and associated print queue become available. Thisapproach can be problematic.

Processing the next print job when only a first downstream processor isready requires measures to prevent damage to the unfinished print job.Print queues and processing in downstream processors for a first jobwould have to be isolated from the second job to prevent the two printjobs from running together. A great many fonts are available for use inprint jobs. On the other hand, most print jobs only use a small numberof fonts. In the system, fonts are associated with a print job and notwith individual documents or frames. The main controller upon receivinga print job, loads required fonts into a font store in memory. The fontstore is accessible by all of the downstream processors and the fontsare used during raster image processing or the like. Fonts can beunloaded when no longer required. The usage of fonts in common for eachprint job greatly reduces required memory space for the fonts, but makesprocessing the next print job, when only a first downstream processor isready, problematic. If the second print job has different fonts, thenthere is a risk that the fonts used for the first print job will bechanged or deleted, while still needed for raster image processing thefirst print job.

FIG. 6 shows an embodiment of the methods described herein that providesjob startup control to resolve these issues. A stream of print jobs isreceived (600) at the main controller. The print jobs are segmented(602). This can occur one-by-one as needed, or otherwise as convenient.Segments of one of a stream of print jobs are distributed (604) to aplurality of downstream processors. The downstream processors may or maynot be all of the available downstream processors, depending upon thecontent of the print job. Each of the downstream processors receives oneof the segments and supplies a respective one or more of the printheads.The remaining print jobs of the stream are sequestered (606), that is,remaining print jobs are set aside, and while set aside are notprocessed by the downstream processors.

The distributed segments are processed (608) in the downstreamprocessors to provide respective printable frames, which are sent to therespective printing module and printed (612) with the associatedprintheads. The processing in different downstream processors isasynchronous and dependent upon content of the respective segments. Eachdownstream processor, immediately after processing a segment, transmits(610) a frame completion signal to the main controller. When the maincontroller determines that the frame completion signals have beentransmitted by all of the plurality of downstream processors used by theprint job, then the sequestering of the next print job of the stream isreleased (614). This process is repeated (616) for each of the jobs inthe stream. The number of segments and the number of downstreamprocessors may differ in each iteration.

In a particular embodiment, the printing of a print job is independentof the transmitting of the frame completion signals of that print job.This has the advantage of simplifying queuing in the print queues.

Sequestration can occur before, during or after the operations performedby the main controller or in some combination. For example, sequesteredprint jobs can be in the form of segments or can be unsegmented. In theformer case, the input queue can precede or follow distribution of thesegments. In the latter case, the sequestered print jobs are unsegmentedand not yet distributed. Intermediate approaches are possible. Therequested print jobs are held in an input queue, which can be providedas physical units of memory or as a logical structure that makes thesequence of sequestered print jobs available when needed.

In a particular embodiment, the main controller loads necessary fonts asa part of distributing segments of a print job. The main controllerunloads other fonts. The sequestering also blocks unloading of theloaded fonts of the print job preceding the sequestered print job. Thereleasing allows unloading of the loaded fonts. When unloading of fontsis blocked, a message can be provided to an operator indicating thatblocking and allowing the operator to override the block. Font unloadingcan also be blocked or allowed based on other parameters, such as theoutput state of a sensor in finishing equipment on-line with the press.Such blocking and allowing can be additive of the blocking and allowingbased on sequestration.

Printing by the different printheads can be synchronized, but it isexpected that, in most cases, printing of some or all of the printheadsis in temporal asynchrony. In other words, the printing of differentframes by such printheads is not synchronized. This results fromdifferences in the content printed by the different printheads, but mayalso be due to other factors. In some cases, the receiver does not havea constant relationship to the different printheads so as toautomatically synchronize the positioning of the document for printingby each of the printheads. For example, as discussed elsewhere herein,the web receiver may be subject to stretching during printing. Withcut-sheet receivers, one or more sheets can be delayed during transport.For example, a transport path that includes a drum that ordinarilycarries the sheets for a single revolution can be modified to carry thesheets on the drum for multiple revolutions. The same effect can beprovided by moving sheets in and out of a temporary storage bin.

FIG. 5 illustrates a specific embodiment of an implementation of asystem that provides job startup control. A stream of print data isreceived by the supervisor of the main controller. In the supervisor, aqueue control unit 141 passes a print job 24 of the stream to a primaryunit 123 or transfers the print job to the input queue 143, in responseto a ready or not ready signal supplied to port 147 that indicateswhether the downstream processors are still processing the previousprint job or are ready for the next print job. The primary unit 123accepts the print job data from the queue control unit 141 until itencounters a start of job statement, which indicates the start of asecond print job. At this point, it outputs a logic level low signal toan AND gate 149, driving its output port 147 low. This causes the queuecontrol unit 141 to stop the transfer of print data at the end of thefirst print job. The primary unit 123 transfers the first print job tothe job record processor 125.

The job record processor 125 identifies which downstream processors133-1 through 133-x will be used to process the print job. The jobrecord processor stores a tally of the downstream processors utilizedfor that print job, in tally memory 151. The job record processor 125then segments the print job and distributes the segments to respectivedownstream processors 133 via a data bus 131. When the segments of theprint job have been distributed, the job record processor sends adistribution completion signal to completion determination unit 149 ofthe main controller. The primary unit 123 can also send a completionsignal, if desired. This signal is redundant of the distributioncompletion signal, but may be useful in isolating errors. The completiondetermination unit 149 is shown and described as an AND gate. It will beunderstood that the specific logic used in implementing these and otherfeatures can be modified, as is well known to those of skill in the art.

The processor buffer 129 can store the distributed segments between therecord processor 125 and the downstream processors 135 until needed. Ineach downstream processor 133, the respective segment is raster imageprocessed, converting the print data into a bitmapped frame. Printbuffers 137 hold the respective bitmapped frames until the frames can beoutput 139 and transferred to the respective printing module.

Each downstream processor 133 is capable of producing a job completesignal 153, to indicate whether the downstream processor is processingthe print job or has completed processing. The job completion signals151-1 through 151-x are supplied via links 157 and 159 to job completiontester 161 in the main controller. The job completion tester 161compares the job completion signals from the downstream processors withthe tally stored in tally memory 151. The job completion tester outputsa logic level high when a job completion signal has been received fromeach of the downstream processors in the tally and otherwise provides alogic level low. FIG. 5 shows the job completion signal 153 as beingderived by a decision block 155. It will be recognized that there arenumerous methods by which the job completion signal 153 can be derived,including but not limited to if-then conditional tests or subroutinescalled upon encountering an end of job reference in the data stream.

By the time the job completion tester 161 outputs a logic level high,the main controller 123 and the job record processor 125 will havealready completed processing of the print job and will have changedtheir output signal to the AND gate 149 to high. With all inputs to theAND gate 149 at logic level high, the AND gate 149 outputs a logic levelhigh, which enables the queue control 120 to start transferring datafrom the input queue 122 for the next print job to the primary unit 123to start the processing of the next print job.

Fast Job Halt

Referring now to FIG. 1, in the press there is a consider distancemeasured along the transport path between the first printhead and thelast printhead. As a result, the first printhead prints a large numberof documents before the first such document arrives at the lastprinthead, which prints on the second side of the document. Similarly,at the end of a print job, the first printhead stops printing longbefore the last printhead stops printing. With high speed printing, theprint queues need to be large. This is particularly the case for highspeed web fed presses, since a large amount of inertia is associatedwith moving the web through the press at high print speeds. Thesepresses cannot quickly stop and restart the motion of the receiver. Forexample, in some presses, it can take thirty seconds to slow a web downfrom 300 m/sec to 60 m/sec in a controlled manner. This requires thedata processing speed to be very fast, and mandates that there be someamount of data ready for printing stored in a buffer should there be amomentary delay in processing the data.

In a data system that allows print jobs to be queued up to print oneafter another without stopping the printer, the need to store printready data in buffers increases. This is due to several constraints onthe data system. There are overhead tasks to be completed at the startof some print jobs before print data can be processed by the downstreamprocessors. One print job may not use the same fonts as the precedingprint job. The fonts must be loaded before the print job can be rasterimage processed. This may necessitate unloading earlier loaded fonts.The overhead tasks add time and, thus, increase print queue sizes. Anadditional constraint is imposed if the above-described job startupcontrol is used. In that case, a first job must be completely bitmappedby all the downstream processors and the bitmapped frames stored inprint queues ready to output to the printheads, before the maincontroller can start to process the second print job. If the transportpath of a web press between the first and last printhead is about 60feet (about 18 meters) long, there is about a 3.6 second delay betweenprinting with the first and last printheads, when printing at high speedof about 1000 ft/min (about 300 m/min). The print queue for the firstprinthead must therefore have data for at least 60 feet of print to keepfrom running out of data.

Due to these various requirements, a considerable amount of bitmappeddata must be stored in the print queues to prevent the press fromrunning out of bitmapped data before the bitmapped data for the secondprint job is available. In a particular embodiment, the print queueshold enough bitmapped frames for 200 feet of printing for each of eightprintheads in the system. This requires about 12 GB of memory. As theprint speed, number of printheads used, width of a printhead, or theresolution of the printheads increase, the sizes of the print queues arefurther increased.

Management of the large amounts of buffer memory required for the printbuffers can become problematic. A particular problem is halting acurrent print job and quickly preparing for printing another print jobor reprinting the current job under different conditions. FIG. 7 is animplementation of an embodiment of the methods described herein,directed to resolving this problem. In this embodiment, a stream of jobdata is received (not shown) in the main controller and a first printjob in the stream is segmented (not shown) and distributed (700), asearlier described, to a plurality of downstream processors. The segmentsare processed (702) and the resulting printable frames are stored (704)in respective print queues. Printing of the first print job is initiated(706). Prior to completion of the printing, a job halt request isreceived (708) in the main controller. The job halt request can beentered by a user via the user interface or can be generated by acomponent of the system, independent of the main controller. Forexample, a sensor could generate a job halt request when a reservoir ofa special ink required for the first print job was empty.

The main controller transmits (710) disable commands to the downstreamprocessors responsive to the job halt request. The downstream processorseach receive a disable command, stop processing, and send (712) anacknowledgement of the respective disable command to the maincontroller. The disable commands can be transmitted in one or moregroups or individually.

In a particular embodiment, the transmitting of the disable commands andthe sending of the acknowledgements is sequential. A first disablecommand is output to a first of the downstream processors, which stopsprocessing the respective segment and returns an acknowledgement. Afterreceiving that acknowledgement, the main controller, in response thensends a disable command to the next downstream processor, which stopsprocessing and sends an acknowledgement. The process iterates for theremaining downstream processors.

It is currently preferred that the disable commands are only sent to theplurality of downstream processors used in processing the current printjob. Disable commands could also be sent to downstream processors notused in the current print job, but such commands and correspondingacknowledgements would be superfluous, except as a convenience, forexample, in providing a count of available downstream processors.

The main controller groups (714) the downstream processors as they stopprocessing and become available into one or more groups. Downstreamprocessors not used in the current print job are also grouped. Eachgroup is tasked with emptying one or more of the print queues associatedwith the grouped downstream processors. The downstream processorsmulti-task to empty (716) those print queues. As available, more thanone downstream processor empties the same print queue. Print queues canbe emptied one-by-one or multiple print queues can be emptied at thesame time. When each acknowledgement is received, another downstreamprocessor is available for use in emptying the print queues and anotherprint queue is available for emptying. The number of downstreamprocessors doing the emptying increases as more acknowledgements arereceived. Downstream processors can be assigned to a single group, whichempties print queues one by one or multiple groups can be created toempty multiple print queues concurrently. The downstream processors canbe assigned and reassigned between groups as available and as neededbased on priorities.

Once the print queues are empty, the main controller distributessegments of the next print job, which is then printed as earlierdescribed. In embodiments in which the receiver is a web, the transportof the web is independent of the job halt request and the disablecommands and is uninterrupted during the steps of the method.

In a particular embodiment, when the downstream processor 33-n receivesa disable command from the main controller, the downstream processorimmediately stops creating any more bitmapped data and outputting anymore data, as shown in FIG. 5. The downstream processor calls for thecreation of a helper task 45. In the helper task 45, availabledownstream processors 47 clear memory units 49 of print queues 43, andplace the cleared memory units 51 in a store of available memory.

Multi-Head Press Data Delivery Rate Control

In high speed and very high speed printing, a continuing problem issupplying data at a rate sufficiently matched to the print engine.Communication bandwidth can be limiting, but the greatest constrainttends to be processing, such as raster image processing, in one or moredownstream processors. This processing is generally limited by thecontent of the data stream. One approach to solving this problem ispausing transport of a receiver through a path until data is available.This approach can be practical with some presses that use a receiver inthe form of cut-sheets, but is problematic with other presses,particularly presses having a receiver in the form of a web, and moreparticularly at high rates of transport. Another approach is torestriction how a print job is input, such that the data renderingprocess can ensure that frames can be converted into printable bitmapsat the full rated speed of the printing system. For example, provisionof pre-ripped images to downstream processors can be required. This isworkable, but greatly encumbers the making any last minute changes. U.S.Pat. No. 6,762,855, which is hereby incorporated by reference, disclosesa system that uses buffer management logic to adjust transport speed ona per-document basis. Control buffers accumulate slack time left overfrom raster image processing non-complex documents and then allocatethat slack time to complex documents to optimize average raster imageprocessing time with the speed of the print engine. This patent does notaddress controlling delivery of data from multiple, queued print jobs toprevent a later print job from damaging an earlier unfinished print job.

A particular embodiment addresses the issue of data delivery managementwith multiple, queued print jobs. Referring now to FIG. 8, in aparticular embodiment, a stream of print jobs is received (not shown)and segmented (not shown), the segments of a first print job in thestream are distributed (800) to each of a plurality of downstreamprocessors and are processed (802) to provide respective printableframes, which are then stored (804) in the individual print queues. Theprintable frames are sequentially printed (806) from the print queues ona continuously transported (808) receiver, such as a web. More detailedaspects of these features are as earlier discussed.

In this embodiment, a maximum printing duration of the print queues isperiodically computed (810) during the printing of the first print joband the transport speed of the receiver is regulated (812) to trend themaximum printing durations toward a predetermined baseline. The sendingof segments of a second print job in the stream to the downstreamprocessors is delayed (814), while the processing of respective segmentsof the first print job is completed by the downstream processors. Thisdelaying is counter to the regulating, since the delaying reduces theprint queues of the first print job non-uniformly relative to thebaseline.

The maximum printing durations are each computed by first estimating aprinting duration of each of the print queues. Each printing durationrepresents a period of time needed to process and/or print therespective printing frames. It is preferred that printing durations lookahead, such that time is available to start ramping the transport speed.A printing duration is estimated for a unit of printable frames. Theunit can be a document, a number of printable frames, or the content ofa print queue.

Each of the printing durations includes a usage time that represents therequired time for completion of printing of the respective unit ofprintable frames. At least one of the printing durations includes slacktime. This is a difference in usage times between two or more of theunits. After the printing durations are estimated, slack time of one ormore of the printing durations is reallocated between units and themaximum of the printing durations is then ascertained. Units can bepaired or otherwise considered in any convenient manner for estimatingslack times and reallocating. For example, highest printing duration canbe paired with lowest, and then next highest and next lowest, and so on.

The reallocating can be within individual print queues or between one ormore print queues or both. In reallocating between print queues,resources are also reassigned. In a particular embodiment, one or moremicroprocessors are reassigned between respective downstream processorsalong with reallocated slack time.

The transport speed is regulated based on a difference between acomputed maximum printing duration and a baseline that is predeterminedfor a particular printing system. The baseline can be a constantpercentage of maximum queue capacity or can be more complex. Forexample, the baseline can vary to account for start-up of components.Changes in transport speed can be designated at each computation of amaximum printing duration. In particular embodiments, each changespecifies a ramp of speeds having a trend of approaching the baseline.Because of the reallocations, the average transport speed of a print jobis likely to be increased, by decreasing the time spent ramping up anddown.

Delaying sending the second print job results in the individual printqueues emptying one after another in an order based on the sequenceorder and relative positions of the respective printheads along thetransport path and on any other variation in printing durations betweenrespective print queues. The emptying of the print queues is non-uniformin terms of printing duration, that is, relative to the baseline. Theprint queues empty as printable frames are printed, but those frames canvary greatly in printing duration. The delaying makes the regulating ofthe transport speed less effective, since less allocating can occur asless print queues hold printable frames.

In a particular embodiment, the processing of the second print job isalso delayed by the loading of fonts for the second print job and, tothe extent necessary, the unloading of fonts from the first print job.The time and resources spent loading and unloading fonts are notavailable for loading the second print job.

In addition to any effects of the delaying on the speed of thetransporter, the main controller also tracks the completion status ofthe print jobs and, if necessary, further slows the rate of receivertransport, as the first print job approaches and reaches completion. Theslower rate provides the time necessary to refill the print queues whenthe second print job is started.

Printing durations can be based on the size of print queues, but this innot preferred, since it does not take into account changes in printingtime resulting from changes in image content. Depending upon the press,it may be necessary to consider printable frame content to preventerrors, such as stitching and registration defects. There can also beother print job requirements not directly related to the printablecontent that change required printing time, such as operating parametersthat impose speed limitations. For example, use of a sorter in afinishing device may require an additional control sequence. EuropeanPatent Application EP0863003 and U.S. Pat. No. 6,318,833 discussed someof the operating parameters that control ink jet printing.

In a particular embodiment, the printing durations and resultingtransport speeds are based on a consideration of both predictedaccumulation of printable frames (indicated by dashed arrow 816 in FIG.8) and printing requirements of the printable frames (indicated bydashed arrow 818 in FIG. 8). In this case, the printing requirements ofeach of the segments are ascertained prior to or at the time ofestimating printing duration. The accumulation of printable frames ineach of the print queues is also predicted. The periodic estimatesconsider both factors. The predicted accumulations “look ahead” toconsider upstream factors, such as the content of upstream queues, suchas respective processing queues and whether the document is still beingreceived by the main controller.

The printing requirements include both printable content of therespective frames and non-image requirements. Printable content is theimage to be printed on respective frame. The image to be printed canaffect transport speed in a variety of ways. For example, with ink jetheads, time for absorption into the receiver and/or partial or completedrying can limit transport speeds differently between a fully printeddocument and a document printed in only a small percentage of theprinting elements.

Non-image requirements relate to how the content is printed and to thephysical dimensions of the document. (This is typically a variationbetween documents and/or print jobs in the direction of travel, but isnot limited to just that dimension.) Specific examples of non-imagerequirements include the number of printheads used, the usageconfiguration of the printheads, and resolution of the printheads. Theusage configuration of the printheads includes the arrangement ofprintheads used and the arrangement of marking elements (for example,ink nozzles in an ink jet printhead) within those printheads. Physicallength of the document can be a function of receiver transport or can bedefined by the spacings of two or more registration cues. In the lattercase, the time required for the press to recognize and register to theregistration cues can place a limit on transport speed.

Different print jobs tend to have different content and, thus, differentcontent-related printing requirements. Different print jobs in a streamof print jobs and different documents within each of those print jobscan have different non-image requirements. With large separation ofprintheads along the transport path, two or more of the print queues cancontain printable frames of different documents of the print job or fromdifferent print jobs. In those cases, the estimated maximum printingdurations periodically determined are each across multiple documents,rather than representing different printable frames of the samedocument. Suitable periods for iterating the estimates can be determinedheuristically based on printing experience with similar jobs. A singleestimate predicting an entire print job would be undesirable, since thevariable overlap of the different documents or different jobs in theprint queues during printing would make such a prediction complex. Asingle estimate would also be unable to account for actual variations intime requirements during the process, such as time to recognize andapply a registration cue.

The invention is inclusive of combinations of the embodiments describedherein. References to “a particular embodiment” and the like refer tofeatures that are present in at least one embodiment of the invention.Separate references to “an embodiment” or “particular embodiments” orthe like do not necessarily refer to the same embodiment or embodiments;however, such embodiments are not mutually exclusive, unless soindicated or as are readily apparent to one of skill in the art. The useof singular and/or plural in referring to the “method” or “methods” andthe like is not limiting.

In the following description, some features are described as “software”or “software programs”. Those skilled in the art will recognize that theequivalent of such software can also be readily constructed in hardware.Because image manipulation algorithms and systems are well known, thepresent description emphasizes algorithms and features forming part of,or cooperating more directly with, the method. General features of thetypes of computerized systems discussed herein are well known, and thepresent description is generally limited to those aspects directlyrelated to the method of the invention. Other aspects of such algorithmsand apparatus, and hardware and/or software for producing and otherwiseprocessing the image signals involved therewith, not specifically shownor described herein may be selected from such systems, algorithms,components, and elements known in the art. Given the description as setforth herein, all additional software/hardware implementation isconventional and within the ordinary skill in the art.

It should also be noted that the present invention can be implemented ina combination of software and/or hardware and is not limited to devices,which are physically connected and/or located within the same physicallocation. One or more of the components illustrated in the figures canbe located remotely and can be connected via a network. One or more ofthe components can be connected wirelessly, such as by a radio-frequencylink, either directly or via a network.

It will be understood that the circuits shown and described can bemodified in a variety of ways well known to those of skill in the art.It will also be understood that the various features described here interms of physical circuits can be alternatively provided as firmware orsoftware functions or a combination of the two. Likewise, componentsillustrated as separate units herein may be conveniently combined orshared. Multiple components can be provided in distributed locations.

In each context, the invention may stand alone or may be a component ofa larger system solution. Furthermore, human interfaces, e.g., thescanning or input, the digital processing, the display to a user, theinput of user requests or processing instructions (if needed), theoutput, can each be on the same or different devices and physicallocations, and communication between the devices and locations can bevia public or private network connections, or media based communication.Where consistent with the disclosure of the present invention, themethod of the invention can be fully automatic, may have user input (befully or partially manual), may have user or operator review toaccept/reject the result, or may be assisted by metadata additional tothat elsewhere discussed (such metadata that may be user supplied,supplied by a measuring device, or determined by an algorithm).Moreover, the methods may interface with a variety of workflow userinterface schemes.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. A printing method controlling delivery of a stream of print jobs to asequence of printheads of a press, the method comprising: distributingsegments of a first print job in the stream to each of a plurality ofdownstream processors; processing respective said segments in each ofsaid downstream processors to provide respective printable frames;storing said printable frames from each of said downstream processors ina respective one of a plurality of print queues, each said print queuesupplying a respective one or more of the printheads; continuouslytransporting a receiver past said printheads; sequentially printing saidprintable frames from said print queues on said transported receiverusing respective said printheads; computing a maximum printing durationof said print queues periodically during said printing; regulating speedof said transporting to trend said maximum printing durations toward apredetermined baseline; and delaying sending segments of a second printjob in said stream to said downstream processors while said processingof respective segments of said first print job is completed by saiddownstream processors, said delaying being counter to said regulating,wherein said delaying reduces said print queues of said first print jobnon-uniformly relative to said baseline.
 2. The method of claim 1wherein said computing further comprises: estimating a printing durationof each of said print queues, at least one of said printing durationsincluding slack time; reallocating the slack time of one or more of saidprinting durations to revise said printing durations; ascertaining saidmaximum of said printing durations following said reallocating.
 3. Themethod of claim 2 wherein said reallocating is within individual saidprint queues.
 4. The method of claim 2 wherein said reallocating isbetween two or more of said print queues.
 5. The method of claim 4wherein said determining further comprises reassigning one or moremicroprocessors between respective said downstream processors along withsaid reallocated slack time.
 6. The method of claim 2 wherein saidestimating further comprises: ascertaining a set of printingrequirements of each of said segments; predicting accumulation of saidprintable frames in each of said print queues during a correspondingperiod of said printing; and determining said printing durations fromrespective said printing requirements and respective said predictedaccumulations.
 7. The method of claim 6 wherein said printingrequirements of said first and second print jobs include and differ inone or more of: number of said printheads utilized, usage configurationof said printheads, resolution of one or more of said printheads, andregistration cue spacing.
 8. The method of claim 6 wherein only one ofsaid first and second print jobs has the printing requirement of beingtwo-sided.
 9. The method of claim 6 wherein said printing furthercomprises printing a registration cue on said receiver, said determiningfurther comprises locating said registration cue, and said printingrequirements of one or more of said printable frames includeregistration with said located registration cue.
 10. The method of claim9 wherein said printing further comprises, prior to said locating,wetting said receiver with marking material and then drying saidreceiver.
 11. The method of claim 6 wherein said predicting furthercomprises maintaining counts of both said printable frames in each ofsaid print queues and registration cue-requiring frames of saidprintable frames, and utilizing said counts in said determining.
 12. Themethod of claim 1 wherein said delaying further comprises ascertainingcompletion of said processing of all of said segments of said firstprint job; and said method further comprises then iterating saiddistributing, processing, storing, transporting, printing, computing,adjusting, and delaying steps as to said second print job and anyremaining said print jobs of said stream.
 13. The method of claim 12further comprising: receiving said stream of print jobs; segmenting eachof said print jobs into respective said segments; and wherein saidprinting of each of said print jobs provides a printed output having oneor more documents and said printing of each said document addsrespective said printable frames in registry.
 14. The method of claim 1wherein said delaying further comprises: sequestering said second printjob and any remaining said print jobs of said stream; transmitting aframe completion signal from each of said downstream processors,immediately after the respective said processing; and releasing saidsequestering of said second print job, following and responsive to thetransmitting of said frame completion signals from all of said pluralityof downstream processors.
 15. The method of claim 14 wherein: saiddistributing further comprises loading one of a plurality of fonts, saidloaded fonts being used by said downstream processors during saidprocessing; said sequestering further comprises blocking unloading ofsaid loaded fonts; and said releasing further comprises allowingunloading of said loaded fonts.
 16. A printing method controllingdelivery of a stream of print jobs to a sequence of printheads of apress, the method comprising: distributing segments of a first print jobin the stream to each of a plurality of downstream processors; rasterimage processing respective said segments in each of said downstreamprocessors to provide respective printable frames; storing saidprintable frames from each of said downstream processors in a respectiveone of a plurality of print queues, each said print queue supplying arespective one or more of the printheads; continuously transporting aweb past said printheads; sequentially printing said printable framesfrom said print queues on said transported receiver using respectivesaid printheads to provide a printed output having one or moredocuments, said printing of each said document adding respective saidprintable frames in registry; estimating a printing duration of each ofsaid print queues, at least one of said printing durations includingslack time; reallocating the slack time of one or more of said printingdurations to revise respective said estimated printing durations;ascertaining a maximum of said printing durations following saidreallocating; computing a maximum printing duration of said printqueues; repeating said estimating, reallocating, and ascertainingperiodically during said printing; regulating speed of said transportingto trend said maximum printing durations toward a predeterminedbaseline; and delaying sending segments of a second print job in saidstream to said downstream processors while said raster image processingof respective segments of said first print job is completed by saiddownstream processors, said delaying being counter to said regulating,wherein said delaying reduces said print queues of said first print jobnon-uniformly relative to said baseline.
 17. The method of claim 16wherein said reallocating is between two or more of said print queuesand said determining further comprises reassigning one or moremicroprocessors between respective said downstream processors along withsaid reallocated slack time.
 18. A printing system comprising: a maincontroller distributing segments of job data; a plurality of downstreamprocessors, each said downstream processor receiving and processingrespective said segments to provide respective printable frames; memorystoring said printable frames from each of said downstream processors ina respective one of a plurality of print queues; a press having aplurality of printheads, each said printhead being supplied by arespective said print queue, said press having a transport unitcontinuously transporting receiver along a path past said printheads,said printheads printing said printable frames from said print queues onsaid receiver using said supplied printheads to provide a printed outputhaving one or more documents, said printing of each said document addingrespective said printable frames in registry; wherein said maincontroller periodically estimates a printing duration of respective saidprintable frames in each of said print queues, optimizes speed of saidtransporting to accommodate all of said printing durations, saidoptimizing reallocating slack time of one or more of said printingdurations, and delays sending segments of a second print job in saidstream to said downstream processors until said processing of all ofsaid segments of said first print job is completed, wherein saiddelaying reduces said print queues of said first print job non-uniformlyduring said optimizing.
 19. The system of claim 18 wherein each of saiddownstream processors transmits a frame completion signal to said maincontroller immediately after the respective said processing; and saidmain controller sequesters said second print job and any remaining saidprint jobs of said stream and then releases said sequestering of saidsecond print job, following and responsive to the transmitting of saidframe completion signals from all of said plurality of downstreamprocessors.
 20. The system of claim 18 wherein: said distributingfurther comprises loading one of a plurality of fonts, said loaded fontsbeing used by said downstream processors during said processing; saidsequestering further comprises blocking unloading of said loaded fonts;said releasing further comprises allowing unloading of said loadedfonts; and said estimating further comprises: ascertaining a set ofprinting requirements of each of said segments; predicting accumulationof said printable frames in each of said print queues during saidprinting; and determining said printing durations from respective saidprinting requirements and respective said predicted accumulations.